Procena sadržaja metala i elemenata u tkivima 4 komercijalne vrste riba iz Dunava kod Beograda

Cilj ovog istraživanja je bio da se proceni akumulacija elemenata u četiri komercijalne vrste riba na dva lokaliteta na Dunavu, u Beogradu. U ovom istraživanju, određene su koncentracije 11 elemenata (As, Cd, Cr, Co, Cu, Fe, Hg, Mn, Ni, Se, i Zn) u tkivima mišića, jetre i škrga sledećih vrsta: mrena (Barbus barbus), deverika (Abramis brama), štuka (Esox lucius) i smuđ (Sander lucioperca). Rezultati su ukazali da je distribucija metala i elemenata u tragovima u različitim tkivima specifična za vrstu. Koncentracije As, Cd, Fe, Hg, i Zn u mišićima riba su bile ispod maksimalno dozvoljenih koncentracija MDK, utvrđenih od strane EU i Republike Srbije. Na osnovu dobijenih rezultata, neophodno je uspostaviti program stalnog monitoringa na Dunavu u Beogradskom regionu

Mapping differential elemental accumulation in fish tissues: importance of fish tissue sampling standardization

The concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se and Zn in the muscle, gills, liver and intestine of the wels catfish (Silurus glanis) from the Danube River were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The aim of the study was to determine whether in complex muscle/skin, gill filament/gill arch, proximal/distal liver and proximal/median/distal intestine samples, particular components differ in concentrations of the analyzed elements. Results indicated that there were no differences in the accumulation of different elements between the proximal and distal liver segments and between the proximal and median intestine sections. Conversely, elemental accumulation patterns in muscle and skin differed significantly. Significant differences were also observed between the gill arch and filaments, as well as between the distal and the two upper intestine sections. Findings indicated the importance of detailed reporting of tissue sampling, i. e. whether the skin was included in the muscle sample, as well as if the gill arch and filaments were analyzed together. Due to a potential bias that can be produced by different muscle/skin or gill arch/filament ratios included in the sample, we strongly recommend that they should not be analyzed together. Results of the present study might be of interest to the scientific community and stakeholders involved in aquatic ecosystem monitoring programs

Strukturiranje i primena materijala na osnovu biopolimera hitozana

Derived from chitin, chitosan is a unique biopolymer that exhibits, beside biocompatibility and biodegradability, outstanding adsorption properties. The layer-by-layer (LBL) deposition technique is based on the alternated adsorption of materials bearing complementary charged or functional groups, in aqueous medium. As a consequence of the polycationic nature of chitosan, chitosan-based films can be used as sensors, drug delivery systems and in tissue engineering. The goal of work was to obtain innovative nano-composites beads based on hitosan, alginate and iron-oxide prepared using LBL deposition method, as magnetic adsorbents used for the separation of dyes from solutions and suspensions.Hitozan je jedinstveni biopolimer koji, pored biokompatibilnosti i biodegradabilnosti, pokazuje i odlična adsorpciona svojstva. Sloj po sloj tehnika (layer-by-layer, (LBL)) se zasniva na naizmeničnoj adsorpciji materijala sa komplementarno naelektrisanim ili funkcionalnim grupama, u vodenoj sredini. Polikatjonska priroda hitozana omogućava njihovu primenu u LBL procesima, i zbog toga se filmovi na osnovu hitozana koriste kao senzori, nosači lekova i u inženjerstvu tkiva. Cilj rada je strukturiranje inovativnih nanokompozitnih granula na osnovu hitozana, alginata i Fe2O3 primenom LBL tehnike radi njihove primene kao magnetnih adsorbenata za uklanjanje boja iz rastvora i iz suspenzija

Hitozan/bentonit granule za tretman otpadnih voda

Aim of this research was synthesis of chitosan/bentonite nanocomposite beads for colored wastewater treatment by adsorption. Influence of preparation procedure on the morphology, adsorption and thermal properties has been studied. It was proved that procedure method affects morphology, as well as enthalpy of absorbed water evaporation, which depends on the molarity of NaOH, and does not affect glass transition temperature. Chitosan adsorption capacity was improved by addition of modified bentonite, which is desirable in colored wastewater treatment.Cilj ovog istraživanja je bila sinteza hitozan/bentonit nanokompozitnih granula za prečišćavanje obojenih otpadnih voda metodom adsorpcije. Proučavan je uticaj postupka pripreme na morfologiju, kao i na adsorpciona i toplotna svojstva nanokompozitnih biopolimera. Dokazano je da način pripreme hibridnih granula utiče na morfologiju, kao i na entalpiju isparavanja adsorbovane vode čija vrednost zavisi od molarnosti NaOH, a ne utiče na temperaturu prelaska u staklasto stanje. Sposobnost adsorpcije hitozana je poboljšana dodavanjem modifikovanog bentonita, koji je poželjan u tretmanu obojenih otpadnih voda

Strukturiranje ekološki prihvatljivih elastomernih kompozitnih materijala

For the waste rubber recycling, it is obligative to know the chemical composition of the waste products, if it is to be used in the new composite elastomeric material formulation. The composite elastomeric materials obtained from the waste rubber powder have a very diverse application (farm floors, sports stadiums, tyres production, in construction as a vibration protection material). The aim of this work was to prepare elastomeric composites based on recycled elastomer powder (REP). A few types of elastomeric materials were synthesized based on natural rubber, polybutadiene rubber, styrene-butadiene rubber, (NR/BR/SBR, 40/40/20 phr), carbon black and recycled elastomer powder were synthesized. It was assessed that composites NR/BR/SBR/REP have shorter optimum curing time tc90 than samples without REP. By increasing the REP content the tc90 value and tensile strength are decreasing, but the abrasion resistance is increasing.Kod recikliranja otpadne gume neophodno je poznavati hemijski sastav otpadnog proizvoda, ukoliko će se on koristiti u recepturama za nove hibridne elastomerne materijale. Kompozitni elastomerni materijali dobijeni od praha otpadne gume imaju veoma raznovrsnu primenu (podovi na farmama, sportski stadioni, dobijanje pneumatika, u građevinarstvu kao materijali za zaštitu od vibracija itd). Cilj ovog rada je bio da se dobiju elastomerni kompoziti na osnovu reciklirane gume. Sintetisano je nekoliko tipova elastomernih materijala na osnovu prirodnog kaučuka, stiren-butadienskog kaučuka i polibutadienskog kaučuka (NR/BR/SBR, 40/40/20 phr), čestica čađi i recikliranog gumenog praha. Ustanovljeno je da kompoziti NR/BR/SBR/REP imaju kraće optimalno vreme umrežavanja u poređenju sa uzorcima NR/BR/SBR bez REP. Porastom količine REP smanjuje se vreme optimalnog umrežavanja i prekidna črstoća, a povećava se otpornost na abraziju

Curing kinetics of alkyd/melamine resin mixtures

Alkyd resins are the most popular and useful synthetic resins applied as the binder in protective coatings. Frequently they are not used alone but are modified with other synthetic resins in the manufacture of the coatings. An alkyd/melamine resin mixture is the usual composition for the preparation of coating called 'baking enamel' and it is cured through functional groups of resins at high temperatures. In this paper, curing kinetics of alkyd resins based on castor oil and dehydrated castor oil with melamine resin, has been studied by DSC method with programmed heating and in isothermal mode. The results determined from dynamic DSC curves were mathematically transformed using the Ozawa isoconversional method for obtaining the isothermal data. These results, degree of curing versus time, are in good agreement with those determined by the isothermal DSC experiments. By applying the Ozawa method it is possible to calculate the isothermal kinetic parameters for the alkyd/melamine resin mixtures curing using only calorimetric data obtained by dynamic DSC runs. Depending on the alkyd resin type and ratio in mixtures the values of activation energies of curing process of resin mixtures are from 51.3 to 114 kJ mol-1. The rate constant of curing increases with increasing the content of melamine resin in the mixture and with curing temperature. The reaction order varies from 1.12 to 1.37 for alkyd based on dehydrated castor oil/melamine resin mixtures and from 1.74 to 2.03 for mixtures with alkyd based on castor oil. Based on the results obtained, we propose that dehydrated castor oil alkyd/melamine resin mixtures can be used in practice (curing temperatures from 120 to 160°C)

Synthesis and curing of alkyd enamels based on ricinoleic acid

A combination of an alkyd resin with a melamine-formaldehyde resin gives a cured enamel film with the flexibility of the alkyd constituent and the high chemical resistance and hardness of the melamine resin at the same time. The melamine resin is a minor constituent and plays the role of a crosslinking agent. In this paper, alkyd resins of high hydroxyl numbers based on trimethylolpropane, ricinoleic acid and phthalic anhydride were synthesized. Two alkyds having 30 and 40 wt% of ricinoleic acid were formulated by calculation on alkyd constant. Alkyds were characterized by FTIR and by the determination of acid and hydroxyl numbers. Then synthesized alkyds were made into baking enamels by mixing with melamine-formaldehyde resins (weight ratio of 70:30 based on dried mass). Two types of commercial melamine resins were used: threeisobutoxymethyl melamine-formaldehyde resin (TIMMF) and hexamethoxymethyl melamine resin (HMMMF). Prepared alkyd/melamine resin mixtures were cured in a differential scanning calorimeter (DSC) under non-isothermal mode. Apparent degree of curing as a function of temperature was calculated from the curing enthalpies. Kinetic parameters of curing were calculated using Freeman-Carroll method. TIMMF resin is more reactive with synthesized alkyds than HMMMF resin what was expected. Alkyd resin with 30 wt% of ricinoleic acid is slightly more reactive than alkyd with 40 wt% of ricinoleic acid, probably because it has the high contents of free hydroxyl and acid groups. The gel content, Tg, thermal stability, hardness, elasticity and impact resistance of coated films cured at 150°C for 60 min were measured. Cured films show good thermal stability since the onset of films thermal degradation determined by thermogravimetric analysis (TGA) is observed at the temperatures from 281 to 329°C. Films based on alkyd 30 are more thermal stable than those from alkyd 40, with the same melamine resin. The type of alkyd resin has no significant effect on the gel content and the hardness of film. Hardness of cured film increases with increasing of Tg. The values of the films elasticity are satisfied for all prepared samples and are independent on the type of alkyd or melamine resin. The impact resistances of coated films are very high